Alarm signal, in zoology, a ritualized means of communicating a danger or threat among the members of an animal group. In many cases the signal is visual or vocal, but some animals—ants, bees, and certain fishes, for example—secrete chemical substances. Alarm communications frequently cross species boundaries. The hawking alarm calls of many small birds are similar and will cause most other birds to take cover. A visual alarm signal, common in mammals, is “flagging,” the lifting of the tail to reveal its white undersurface. The white fur shows only in fright situations when the animal raises its tail as it bounds away. Biologists do not agree about the exact meaning of this common mammalian alarm response. While the alarm reaction usually takes the form of a freeze-or-flight response, it may, if the stimulus is within a critical distance, elicit an attack.

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Alarm calls and other complex signaling behaviour within aggregations can also reduce the likelihood of predation. Calls may coordinate a group’s escape from danger, confuse a predator, and prompt individuals to seek protected sites or shelter. Group members presumably benefit because the overall risk of a successful predation attempt is reduced. Alarm calls may also convey information about...

...of birds and mammals effectively and specifically evoke avoidance patterns. In some cases, learning clearly emerges as a factor; thus, members of a colony of birds seem to learn to respond to the alarm calls of all species present in the colony. Among ducklings, a visual model to evoke fleeing and hiding can be fashioned as a cardboard cutout. When moved overhead in one direction, the model...